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RE: Obdurodon (was Re: Coronosaurus, new ceratopsid genus for Centrosaurus brinkmani)



Tim Williams wrote-

> You may be using the term more "aquatic" more rigidly than I am. I'm
> also using the term to include littoral/shore-dwelling birds.
> Hongshanornithids (_Hongshanornis_, _Parahongshanornis_,
> _Longicrusavis_) have features consistent with wading, particularly in
> the hindlimbs and pedes. _Archaeorhynchus_ has a beak reminiscent of
> a spoonbill. To me, the _Yanornis_ skull appears adapted for
> fish-eating. As you say, we know that _Yanornis_ ate fish; and based
> on preserved remains of small teleosts close to the stomach,
> _Jianchangopteryx_ may have eaten fish as well (on this basis, the
> original description suggested it was piscivorous). Plus we have more
> crownward taxa such as _Gansus_ and the Hesperornithes, which like you
> said were undoubtedly aquatic. I would regard _Ichthyornis_ as
> aquatic, especially if the reconstruction of this taxon a tern-like
> bird is correct.

Then yes, our definitions differ.  I don't think ornithologists would call 
sandpipers or gulls aquatic or amphibious.  Maybe hongshanornithids were 
littoral, but the characters cited by O'Connor et al. (2010) are problematic- 
just because a dorsal supracondylar process on the humerus is also present in 
charadriiforms, does that make it a littoral feature?; Concornis and Gobipteryx 
have tibiotarsi as long as some hongshanornithids; taxa like Archaeopteryx, 
Sapeornis and Sinornis can have as elongate of proximal pedal phalanges as 
Longicrusavis; Apsaravis and ratites have even more reduced halluces.  
Archaeorhynchus' premaxilla is only described as "broad with a slightly rounded 
margin", while the dentary is said to be "spathulate".  The authors compare it 
to a duck, but then note the many gastroliths probably indicate it ate plants.  
Terrestrial plants we can assume, as aquatic ones aren't hard enough to require 
gastroliths, right?  Maybe it was more like geese?  The fish remains in 
ornuthuromorphs aren't useful, as we know Confuciusornis ate fish and had no 
more littoral adaptations than standard Yixian enantiornithes.

> Of course, by no means all basal ornithuromorphs were aquatic; some
> were certainly not (_Patagopteryx_, _Apsaravis_, etc). But basal
> Ornithuromorpha does seem crowded with putative aquatic/amphibious
> birds, even if the criteria for identifying a particular bird as
> "aquatic" can be vague. By contrast, although there are putative
> aquatic enantiornitheans, they are exceptional in this regard (among
> Enantiornithes) and many more show highly refined perching abilities
> suggesting they were specialized arborealists.

I'd agree enantiornithines are usually more adapted to perching than basal 
ornithuromorphs, and some of the latter were littoral (Ichthyornis, Yanornis?) 
and others were aquatic (Gansus, hesperornithines), but others were fully 
terrestrial (Patagopteryx, Archaeorhynchus?, Gargantuavis, Apsaravis) and the 
rest need further study to determine where they fall on the 
terrestrial-littoral line.

Mickey Mortimer